DummyActivity.java

public class DummyActivity extends ActionBarActivity {

    File f;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.dummylayout);

        // This image exists
        f = new File(getFilesDir(), "abc.png");

        final ImageView image = (ImageView) findViewById(R.id.imageView);
        Button loadBtn = (Button) findViewById(R.id.load);
        Button invalidateBtn = (Button) findViewById(R.id.invalidate);
        Picasso.with(DummyActivity.this).load(f).into(image);

        loadBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Picasso.with(DummyActivity.this).load(f).into(image);
            }
        });

        invalidateBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Picasso.with(DummyActivity.this).invalidate(f);
            }
        });
    }


}